In the case where a circular hole is provided to an object to be worked such as aluminum cast by machining, an edge is formed on a peripheral edge of the circular hole, and a burr occurs around the edge. In order to remove such a burr and chamfer the edge, a chamfering tool 10 shown in FIGS. 8(a) and 8(b) is conventionally used. The chamfering tool 10 is a rotational tool, and is composed of a shank section 11 fixed to a rotational chuck, and a circular truncated cone-shaped cutting section 12 provided integrally with a forward end 11a of the shank section 11. The cutting section 12 is provided with a blade section 121 on an outer peripheral surface 12a so that the blade section 121 faces a rotating direction (direction of an arrow in the drawings). The blade section 121 can remove a burr occurring on the edge E of an object to be worked which is brought into contact with the blade section 121 and chamfer the edge E.
Patent Literature 1: Japanese Patent Application Laid-Open No. 11-104916 (1999).
An angle of a cutting face 121a of the blade section 121 is tilted to the rotating direction so that a chip generated due to a burring work and a chamfering work is discharged outside from the blade section 121. The chip is discharged to the side of the shank section 11 (upper side in FIGS. 8(a) and 8(b)) or a side opposite to the side of the shank section 11 (lower side in FIGS. 8(a) and 8(b)) due to the tilt angle of the cutting face 121a. That is to say, when the cutting face 121a is tiled so as to face the side of the shank section 11, as shown in FIG. 8(a), the chip is discharged to the side of the shank section 11. When the cutting face 121a is tiled so as to face the side opposite to the side of the shank section 11, as shown in FIG. 8(b), the chip is discharged to the side opposite to the side of the shank section 11.
The chip discharged out of the blade section 121 is not always separated from the object to be worked W completely, and as shown in FIGS. 8(a) and 8(b), they occasionally remain as secondary burrs B1 and B2. Since the secondary burrs B1 and B2 deteriorate the quality and the safety of products, they should be eliminated completely. In the case where, however, the secondary burrs are removed by the chamfering tool 10, it is necessary to move a position of the chamfering tool 10 and change its angle with respect to the edge E, thereby making working facility complicated. Further, when another chamfering tool is used, another working facility is required, thereby causing an increase in facility space.